This application relates to and claims a priority from the corresponding Japanese Patent Application No. 2001-373345 filed on Dec. 6, 2001.
1. Field of the Invention
The present invention relates to a color sorting apparatus for granular objects such as wheat or rice grains and resin pellets in which colored objects or foreign matters mixed in the raw granular objects are sorted out, and more particularly to a color sorting apparatus which is further capable of sorting out such magnetic metal as an iron piece also mixed in the raw granular objects.
2. Description of the Related Art
A typical conventional color sorting apparatus to which the present invention relates comprises a storage hopper for storing therein raw granular objects; a transferring means which includes a vibration feeder arranged beneath the storage hopper and an inclined or slanted flow chute arranged at an exit side of the vibration feeder; at least one optical detection means which is arranged around a falling locus of the raw granular objects released from a lowermost end of the inclined flow chute and which is constituted by a light source, a background and a light receiving sensor; a determination means which outputs an ejection signal based on an optical detection signal from the light receiving sensor; and a sorting means which sorts out a detected unacceptable granular object upon receipt of the ejection signal from the determination means. In the above color sorting apparatus, each raw granular object naturally falling down along the falling locus of the granular objects is illuminated by the light source, the determination means determines the existence of the granular objects to be sorted out based on the changes in the light amount obtained from each granular object, and the granular objects determined as unacceptable ones are sorted out by the sorting means. In this way, the colored granular objects and the foreign matters are removed from the acceptable granular objects. However, among the foreign matters, magnetic metal such as an iron piece cannot be effectively removed by the above conventional color sorting apparatus.
A color sorting apparatus equipped with a device for removing magnetic metal pieces mixed in the raw granular objects which pieces cannot otherwise be removed by the conventional color sorting apparatus is disclosed in, for example, Japanese Utility Model Registration Publication No. Sho 56-277. The publication discloses a color sorting apparatus in which a magnet is suspended over the flow passage of the vibration feeder with a predetermined distance kept from the bottom part of the flow passage in such a manner that any magnetic metal piece is magnetically attracted and removed from the flow of raw granular objects to prevent such magnetic metal piece from flowing to the following flow chute.
However, there has been a following problem in the color sorting apparatus disclosed in the above publication. The removal of the magnetic metal pieces that have been attracted by and caught on the magnet suspended within the vibration feeder should be performed under the condition that the magnet itself is once taken out outside the apparatus after the arm member suspending the magnet is pivotally rotated about the axis thereof. Since the interruption of the transferring of the raw granular objects during the removal operation of the magnetic metal is necessitated in the above conventional method, there is a problem in that the operation efficiency of the granular object color sorting apparatus is inevitably lowered.
An object of the present invention, therefore, is to overcome the problems existing in the prior art, and to provide a granular object color sorting apparatus which is capable of effectively sorting out any magnetic metal pieces mixed in the raw granular objects without lowering the operation efficiency of the color sorting apparatus.
According to one aspect of the invention, there is provided a color sorting apparatus for granular objects, comprising:
a storage hopper for storing therein raw granular objects;
a transferring means for transferring the raw granular objects consecutively to an optical detection point, the transferring means including a magnetic metal removing means having a hollow feeding roll for sending out the raw granular objects stored in the storage hopper; a magnet arranged within the hollow portion of said feeding roll at a raw granular object sending-out side of the feeding roll such that the magnet closely opposes to a part of an inner surface of the feeding roll so as to form a magnetic force active surface on a corresponding part of an outer surface of the feeding roll, the magnetic force active surface attracting magnetic metal mixed in the raw granular objects; and a magnetic metal piece collecting means for collecting the magnetic metal which is released from the outer surface of the feeding roll other than said magnetic force active surface;
an optical detection means arranged around a falling locus of the raw granular objects released from the transferring means, the optical detection means comprising an illuminating means, a background plate and a light receiving sensor for receiving light from the background plate and each of the raw granular objects at the optical detection point, the illuminating means irradiating the background plate and the granular object at the optical detection point;
a determination means for determining as to whether each of the raw granular objects is an acceptable one or an unacceptable one which should be sorted out based on the comparison between a light received signal from the light receiving sensor and a predetermined threshold value, and for outputting an ejection signal when determined as an unacceptable one; and
a sorting means for sorting out the unacceptable one in accordance with the ejection signal from the determination means.